Fix BigInt Serialization Issues in JSON Responses

Problem

The original implementation was encountering serialization errors when attempting to return responses containing BigInt values. This occurred because BigInt values cannot be directly serialized to JSON.

Changes Made

1. Added explicit string conversion for BigInt fields in the response objects:

   • paymasterVerificationGasLimit
   • paymasterPostOpGasLimit

2. Created a serializedResult object that converts BigInt values to strings before JSON serialization:

const serializedResult = {
    ...result,
    paymasterVerificationGasLimit: result.paymasterVerificationGasLimit?.toString(),
    paymasterPostOpGasLimit: result.paymasterPostOpGasLimit?.toString()
};

Testing

Verified that API responses now successfully serialize without errors
Confirmed compatibility with both EntryPoint versions
Added console.log statements to help with debugging response data

Impact

This change ensures proper handling of BigInt values in the paymaster API responses while maintaining the expected response format for clients. The modification is backward compatible and improves the reliability of the service.
Please review and merge these changes to resolve the serialization issues.